This research will assess alterations in the state of ion selective channels in membranes of lobster giant axons induced by sensitized photochemical modification, using the double sucrose gap voltage clamp technique. Axons will be treated with sensitizers, illuminated with visible light, and rate constants for change in excitability parameters will be used as an assay. Experiments will focus on the chemical nature of the target for the process using enhancers and quenchers of singlet oxygen, sensitizers known to be specific for the modified chemical moiety, and simultaneous application of group-specific reagents.